1
general::
Phrase(s): take someone down a notch (or two)
Go to take someone down a peg (or two) and take someone down a notch (or two); knock someone down a peg (or two); knock someone down a notch (or two)
McGrawhill's American Idioms And Phrasal Verbs
2
general::
Also, take down a peg. Deflate or humble someone, as in He's so arrogant that I wish someone would take him down a notch, or That defeat took them down a peg. Both notch and peg in this idiom allude to a series, the former of indentations, the latter of knobs, used to raise or lower something. Specifically, peg alludes to the pegs used to lower a ship's colors. Their figurative use dates from the second half of the 1600s. Also see CUT DOWN, def. 4.
American Heritage Idioms